The present invention relates generally to brake valves for use in vehicle hydraulic systems, and more particularly, to such brake valves of the type which include a manually movable valve member.
Furthermore, the brake valve of the present invention is especially advantageous when used in a vehicle hydraulic system in which the brake valve is connected hydraulically in parallel with another circuit, such as the vehicle power steering system, with both the brake valve and the steering circuit being supplied with pressurized fluid from a common fluid source.
Brake valves of the type to which the present invention relates typically have two operating modes. In a "powered" brake mode, the brake valve communicates pressurized fluid from the source to a brake actuator. In a "manual" brake mode, there is no external source of pressurized fluid available, and movement of the valve spool, by depressing the brake pedal, moves a piston arrangement to generate pressurized fluid for the brake actuator. An example of such a brake valve is illustrated in U.S. Pat. No. 3,166,890, assigned to a predecessor-in-interest of the assignee of the present invention, and incorporated herein by reference.
Increasingly, vehicles utilizing brake valves of the type to which the invention relates have also been utilizing load sensing hydraulic (hydrostatic) power steering systems, and load sensing fluid sources. An example of such a load sensing vehicle hydraulic system is illustrated and described in detail in U.S. Pat. No. 4,043,419, assigned to the assignee of the present invention, incorporated herein by reference.